MySQL创建计算字段

拼接两个列

select concat (vend_name, '(', vend_country,')') 
from vendors 
order by vend_name;

使用别名

///as别名，rtrim 右边空格去除 ltrim左边空格去除 trim两边空格去除
select concat (rtrim(vend_name), ' (', rtrim(vend_country),')') as vend_title 
from vendors 
order by vend_name;

算数计算

select prod_id, quantity, item_price, quantity*item_price as expanded_price 
from orderitems 
where order_num = 20005;